|Publication number||US4551772 A|
|Application number||US 06/594,263|
|Publication date||Nov 5, 1985|
|Filing date||Mar 28, 1984|
|Priority date||Mar 28, 1984|
|Publication number||06594263, 594263, US 4551772 A, US 4551772A, US-A-4551772, US4551772 A, US4551772A|
|Inventors||David E. Sliger|
|Original Assignee||Storage Technology Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Non-Patent Citations (2), Referenced by (41), Classifications (12), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to magnetic recording and more particularly, to a driver circuit for producing bi-directional write current through a magnetic head.
In magnetic recording, the magnetic write head is commonly driven with current in one direction or the other through the head winding to produce bi-directional recording. In magnetic tape systems, it has been common practice to use a write head with a center tap which was connected to reference potential. This produced voltage excursions on both sides of the write head winding which were equal and opposite. The equal and opposite voltage excursions minimized the feed through of transients to the read head circuit. Because the voltage excursions were equal and opposite, the transients which are capacitively coupled to the read circuit are equal and opposite and tend to cancel.
Recently, thin film resistives have been developed for magnetic recording, particularly magnetic tape recording. These heads are produced by a photoresist process. For several reasons, it is not practical to provide a center tap on the head. For one reason, this requires a manual step which is not compatible with the high speed photoresist deposition of the heads.
"PREDRIVER FOR `H` CONFIGURED WRITE DRIVER FOR MAGNETIC RECORDING", by J. A. Bailey, R. G. Black, Jr., and J. Lewkowicz, IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 23, No. 11, Nov. 1981, shows a write driver for a thin film magnetic write head. The driver transistors are connected in an H-configuration with two driver transistors being turned on to produce current through the head in one direction, and the other being turned on to provide current through the head in the other direction. In such a circuit, the voltage excursions on the two sides of the head are not equal and opposite. Because of this, transients are capacitively coupled to the read circuitry.
It is an object of the present invention to provide a write driver circuit for a thin film magnetic head which has an artificial center tap and which reduces feed through of transients to the read circuit.
In accordance with the present invention, current mirror transistors are connected in parallel with the driver transistors in a write driver circuit having an H-configuration. Resistors are connected across the magnetic head with a source of reference potential connected at their junction to create an artificial center tap for the head. The voltage excursions across the head are equal and opposite with respect to the reference voltage. The current mirror transistors produce current flow in a path parallel to the head to maintain the current flow through the two driving transistors equal.
The foregoing and other objects, features and advantages of the invention will be better understood from the following more detailed description and appended claims.
FIG. 1. shows the write driver circuit of the present invention;
FIGS. 2A-2D are waveforms depicting the operation of the present invention; and
FIGS. 3A-3D are waveforms depicting the operation of the prior art.
FIG. 1 depicts a thin film magnetic write head 11 which is driven by first and second driving transistors 12 and 13, and third and fourth driving transistors 14 and 15.
In order to produce current flow through the write head 11 in one direction, the VMOS switching transistor 16 is turned on by a switching signal designated IW. When switching transistor 16 is turned on, current flows through the emitter and base of driving transistor 12, through write head 11, and through driving transistor 13, and the switching transistor 16.
In order to produce current flow in the other direction through head 11, VMOS switching transistor 17 is turned on by the switching signal designated +IW. This produces current flow through driver transistor 14, through the write head 11, through the driver transistor 15, and switch 17.
In accordance with the present invention, write head 11 has an artificial center tap created by two resistors 18 and 19, the junction of which is connected to reference potential, in this case, ground. In order to maintain the voltage excursions on both sides of the head 11 equal and opposite, current mirror transistors 20-23 are provided. First and second current mirror transistors 20 and 21 are connected in parallel with first and second driver transistors 12 and 13. Third and fourth current mirror transistors 22 and 23 are connected in parallel with third and fourth driver transistors 14 and 15. The current flow of the current mirror transistors is parallel to, not through, write head 11. The current mirror transistors maintain the voltage excursions across the head equal and opposite. When driver transistors 12 and 13 are conducting, the current flow through transistor 12 is equal to the current flow through transistor 13. Conversely, when driver transistors 14 and 15 are conducting, current mirror transistors 22 and 23 maintain the current flow through driver transistor 14 equal to that through driver transistor 15.
Transistor 24 is biased so that it is normally conducting. It provides base current to the driver transistor 13 and to the current mirror transistor 21. Similarly, transistor 25 is biased so that is is normally conducting. It provides base current to the current mirror transistor 23 and the driver transistor 15.
The operation of the circuit can be better understood with reference to the waveforms of FIGS. 2A-2D. Assume that +V is +15 volts and -V is -15 volts. FIG. 2A shows the voltage on the left side of head 11 and FIG. 2C shows the voltage on the right side of head 11. FIGS. 2B and 2D show the transients developed by these voltages. Referring to FIG. 2A, when driver transistors 12 and 13 are turned on by switch 16, the voltage at the left-hand side of write head 11 makes an excursion to approximately +15 volts.
Referring to FIG. 2C, the voltage of the right-hand side of write head 11 makes an excursion to approximately -15 volts. The excursions are equal and opposite. When driver transistors 12 and 13 are turned off, and driver transistors 14 and 15 are turned on, the left side of write head 11 (Fig. 2A) undergoes a negative excursion and the right side of head 11 (FIG. 2C) undergoes an equal and opposite positive excursion.
Capacitive coupling exists between the write head 11 and the read head. This capacitive coupling would normally tend to couple the transients shown in FIG. 2B to the read head as a result of voltage excursions on the left-hand side of the write head 11. Similarly, the transients shown in FIG. 2D would tend to be coupled to the read head as a result of voltage excursions on the right-hand side of write head 11. Note that the transients in FIGS. 2B and 2D and equal and oppoosite. They tend to cancel thereby reducing transient feed-through.
On the other hand, consider the waveforms of FIG. 3A-3D which similarly depict the operation of an H-driver circuit without the artificial center tap and current mirrors of the present invention. Without the circuit of the present invention, the voltage on both sides of the write head undergoes a voltage excursion in the same direction. That is, when two drivers are turned on to produce the positive excursion on the left side of the head as shown in FIG. 3A, the right hand side of the head (FIG. 3C) also goes positive with the difference between the three excursions producing current flow.
Similarly, when the other pair of driving transistors is turned on, the left side of the head will undergo a negative excursion as shown in FIG. 3A and the right hand side (FIG. 3C) will undergo a negative excursion of larger magnitude. The capacitively coupled transients are shown in FIGS. 3B and 3D. Note that the transients are cumulative, they do not cancel.
In accordance with present invention, a right driver circuit is provided with substantially reduced feed through of transients to the read head.
While a particular embodiment of the invention has been shown and described, various modifications are within the true spirit and scope of the invention. The claims are, therefore, intended to cover all such modifications.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4015290 *||Jul 31, 1975||Mar 29, 1977||Sangamo Electric Company||Low power recording instrument with two or more tracks|
|US4477846 *||Dec 21, 1981||Oct 16, 1984||International Business Machines Corporation||Sensitive amplifier having a high voltage switch|
|US4489285 *||Apr 7, 1983||Dec 18, 1984||Hitachi, Ltd.||Signal processing circuit employing an improved composite current mirror circuit/device|
|1||"Predriver for `H` Configured Write Driver for Magnetic Recording", J. A. Bailey, R. G. Black, Jr. and J. Lewkowicz, IBM Technical Disclosure Bulletin, vol. 23, No. 11, Apr. 1981.|
|2||*||Predriver for H Configured Write Driver for Magnetic Recording , J. A. Bailey, R. G. Black, Jr. and J. Lewkowicz, IBM Technical Disclosure Bulletin, vol. 23, No. 11, Apr. 1981.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US4639794 *||Jun 19, 1984||Jan 27, 1987||Fuji Photo Film Co., Ltd.||Multiply pulsed magnetic recording|
|US4816932 *||Nov 7, 1986||Mar 28, 1989||Archive Corporation||Circuit for providing a symmetric current to the head of a magnetic recording device|
|US5282094 *||May 26, 1993||Jan 25, 1994||Vtc Inc.||Current mirror having a base current compensation circuit with a compensation mirror and a voltage clamp|
|US5287231 *||Oct 6, 1992||Feb 15, 1994||Vtc Inc.||Write circuit having current mirrors between predriver and write driver circuits for maximum head voltage swing|
|US5291069 *||Dec 15, 1992||Mar 1, 1994||International Business Machines Corporation||Bipolar H write driver|
|US5291347 *||May 26, 1993||Mar 1, 1994||Vtc Inc.||Write driver with H-switch synchronizing transistors|
|US5297024 *||Dec 1, 1992||Mar 22, 1994||Sgs-Thomson Microelectronics, Inc.||Voice coil driver with variable gain in seek and track-follow modes|
|US5309347 *||Sep 18, 1992||May 3, 1994||Sgs-Thomson Microelectronics S.R.L.||H-bridge circuit with protection against crossover conduction|
|US5398144 *||Feb 25, 1993||Mar 14, 1995||Vtc Inc.||Bias generator for a low voltage differential read amplifier|
|US5668676 *||Jun 9, 1995||Sep 16, 1997||U.S. Philips Corporation||Magnetic head write amplifier including current mirrors and switchable current sources|
|US5701213 *||Sep 12, 1996||Dec 23, 1997||Sgs-Thomson Microelectronics, Inc.||Symmetrical resistive transducer biasing circuit and method|
|US5770968 *||Dec 30, 1994||Jun 23, 1998||Sgs-Thomson Microelectronics, Inc.||Differential amplifier with proxy load for control of output common mode range|
|US5790336 *||Jul 15, 1997||Aug 4, 1998||U.S. Philips Corporation||Arrangement comprising a magnetic write head, and write amplifier with capacitive current compensation|
|US5834965 *||Dec 4, 1996||Nov 10, 1998||U.S. Philips Corporation||Circuit for switching current in a mainly inductive load|
|US5994951 *||Jan 20, 1998||Nov 30, 1999||Vtc Inc.||Automatic-tuning circuit for integrated continuous-time MOSFET-C filters|
|US6040954 *||Apr 17, 1997||Mar 21, 2000||International Business Machines Corporation||High speed write driver for magnetic inductive write head using a half-switched H-driver|
|US6101052 *||Jun 14, 1993||Aug 8, 2000||International Business Machines Corporation||H configuration write driver circuit with integral component fault detection|
|US6201653||Jun 12, 1998||Mar 13, 2001||International Business Machines Corporation||By-pass write drivers for high-performance data recording|
|US6222695||Aug 10, 1998||Apr 24, 2001||Siemens Microelectronics, Inc.||System and method for a preamplifier write circuit with reduced rise/fall time|
|US6388476 *||Jan 9, 1997||May 14, 2002||Texas Instruments Incorporated||Self-switched cascode write driver|
|US6456148||Apr 20, 2001||Sep 24, 2002||Stmicroelectronics, Inc.||Circuit and method for writing to a memory disk|
|US6504666||Aug 30, 2000||Jan 7, 2003||Stmicroelectronics, Inc.||Write head driver circuit and method for writing to a memory disk|
|US6512649 *||Aug 30, 2000||Jan 28, 2003||Stmicroelectronics, Inc.||Method for differentially writing to a memory disk|
|US6857937||May 30, 2002||Feb 22, 2005||Komag, Inc.||Lapping a head while powered up to eliminate expansion of the head due to heating|
|US6970316||Nov 9, 2001||Nov 29, 2005||Stmicroelectronics, Inc.||Write head driver circuit and method for writing to a memory disk|
|US7119990||Feb 3, 2003||Oct 10, 2006||Komag, Inc.||Storage device including a center tapped write transducer|
|US7184232||Sep 18, 2003||Feb 27, 2007||Texas Instruments Incorporated||Apparatus and method for driving a write head|
|US7277245||Mar 28, 2005||Oct 2, 2007||Marvell International Ltd.||Write driver circuit for magnetic data storage systems|
|US7280300||Mar 28, 2005||Oct 9, 2007||Marvell International Ltd.||Write driver circuit for magnetic data storage systems|
|US7417817 *||Mar 18, 2003||Aug 26, 2008||Marvell International Ltd.||Write driver circuit for magnetic data storage systems|
|US7880989||Aug 22, 2008||Feb 1, 2011||Marvell International Ltd.||Write driver circuit for magnetic data storage systems|
|US7911736||Mar 22, 2011||Wd Media, Inc.||Storage device and method of using a head that has a concave surface when powered down|
|US20030090828 *||Nov 9, 2001||May 15, 2003||Alesandro Venca||Write head driver circuit and method for writing to a memory disk|
|US20040075942 *||May 30, 2002||Apr 22, 2004||Bajorek Christopher H.||Lapping a head while powered up to eliminate expansion of the head due to heating|
|US20050073340 *||Sep 18, 2003||Apr 7, 2005||Motomu Hashizume||Apparatus and method for driving a write head|
|US20050164607 *||Jan 28, 2005||Jul 28, 2005||Bajorek Christopher H.||Lapping a head while powered up to eliminate expansion of the head due to heating|
|EP0538618A2 *||Sep 14, 1992||Apr 28, 1993||SGS-THOMSON MICROELECTRONICS S.r.l.||An H-shaped bridge circuit with protection against crossover conduction during the reversal of the current in the load|
|EP0720285A2 *||Dec 22, 1995||Jul 3, 1996||Sgs-Thomson Microelectronics, Inc.||Differential amplifier with proxy load for control of output common mode range|
|EP1187102A2 *||Aug 24, 2001||Mar 13, 2002||SGS-THOMSON MICROELECTRONICS, INC. (a Delaware corp.)||Method for differentially writing to a memory disk|
|WO1995035564A2 *||Jun 6, 1995||Dec 28, 1995||Philips Electronics N.V.||Arrangement for recording an information signal on a magnetic record carrier|
|WO1995035564A3 *||Jun 6, 1995||Feb 15, 1996||Philips Electronics Nv||Arrangement for recording an information signal on a magnetic record carrier|
|U.S. Classification||360/46, G9B/5.026|
|International Classification||G11B5/00, G11B5/02, H03K17/66|
|Cooperative Classification||G11B5/02, G11B5/022, G11B2005/001, H03K17/663|
|European Classification||G11B5/02A, H03K17/66B2C, G11B5/02|
|Mar 18, 1985||AS||Assignment|
Owner name: STORAGE TECHNOLOGY CORPORATION 2270 SOUTH 88TH STR
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:SLIGER, DAVID E.;REEL/FRAME:004373/0874
Effective date: 19840316
|Dec 23, 1988||FPAY||Fee payment|
Year of fee payment: 4
|Apr 19, 1993||FPAY||Fee payment|
Year of fee payment: 8
|Jun 10, 1997||REMI||Maintenance fee reminder mailed|
|Nov 2, 1997||LAPS||Lapse for failure to pay maintenance fees|
|Jan 13, 1998||FP||Expired due to failure to pay maintenance fee|
Effective date: 19971105